The promise was made in a meeting at the premier's official residence, the day after the Iranian oil minister began a visit to Japan, a Japanese official said.

In the meeting, Mori noted that Iran was the third biggest supplier of oil to Japan and was an "important country from the viewpoint of stable oil supplies," according to the official.

Namdar-Zangheneh replied that stable supplies of oil to Japan which he termed as a "friendly country" were "especially important," the official said.

The Iranian minister also met Takeo Hiranuma, the Japanese minister of economy, trade and industry.

The two ministers agreed that the two countries should cooperate in the energy field following on from agreement which was reached last November when Iranian President Mohammad Khatami made a historic visit here.

At that time, Khatami offered Japan preferential rights in developing the enormous Azadegan oilfield in south-west Iran, which has reserves of 26 billion barrels.

Japan in return agreed to extend Iran a trade credit line worth three billion dollars over the next three years.

The agreement on exclusive negotiating rights was signed during Khatami's visit. Zangheneh's latest trip comes in the wake of the Iranian parliament agreeing in January to authorise foreign investments in the Azadegan reserves.

Namdar-Zangheneh is using the current trip tp study "ways for greater oil cooperation" between Japan and Iran, according to the Iranian oil ministry.

Iran is seeking to spread its sources of investment in its oil and gas industry, which have so far been mainly western, and European in particular, by attracting Asian nations led by Japan to play a more active role in its oil projects.

Japan is the main economic partner in Asia for Iran, which is the second largest oil producer in the Organization of Petroleum Exporting Countries (OPEC).—AFP.